https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125230
--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Rainer Deyke from comment #5) > This is problematic because "importable header" is never defined. It can > reasonably mean "any header" in a compiler that compiles header units on > demand, in which case my header-only library cannot work at all. I believe > this is a defect in the standard. It's defined in 10.3 [module.import] paragraph 5: "An importable header is a member of an implementation-defined set of headers that includes all importable C++ library headers (16.4.2.3)." And 16.4.2.3 [headers] p2 says: "The headers listed in Table 24, or, for a freestanding implementation, the subset of such headers that are provided by the implementation, are collectively known as the importable C ++ library headers."
